Opiates and opioid peptides modify immune function. Thus exposure to opiates may be a cofactor determining the susceptibility to HIV infection. This application seeks to elucidate the role of opiates and opioid peptides in thymocyte activation and maturation by characterizing the expression of proenkephalin (PEA) mRNA . The underlying hypothesis is that thymic PEA mRNA and the enkephalin peptides are involved in the regulation of activation in both adult and fetal thymus and, therefore, exposure, to opiates may have serious consequences for the establishment of normal cell-mediated immunity. I. Descriptive experiments concerning PEA mRNA expression in adult CD4 thymocytes following activation with the mitogen concanavalin-A (Con-A) will include studies of (a) the kinetics of its expression, (b) the effect of Con A in the rate of synthesis of PEA mRNA, (c) the relationship with PEA mRNA expression and cell proliferation, (d) whether antigen presenting cells (APC) and specific cytokines are required for its expression and (e) the thymic cell subpopulation(s) which express 1.4kb PEA mRNA vs. those expressing the 1.7kb, both of which are induced by Con-A in adult mixed thymocyte cultures. II.The expression of PEA mRNA in fetal thymocytes will also be studied by dot blot analysis of poly A RNA isolated from fetal thymocytes at each day of gestation from day 14 through 18. Both constitutive (day 15) and inducible (day 18) expression of PEA mRNA will be examined and the role and PEA mRNA in fetal thymocyte maturation will be assessed. The particular thymocyte subpopulation expressing PEA mRNA at different stages of gestation will be identified. III. Regulation of PEA mRNA expression in both adult and fetal thymocytes will first be studied by examining the inhibitory effect of IL-1-beta on PEA mRNA expression. A role for enkephalin peptides in IL-1 enhancement of Con-A activation is hypothesized. This will be examined by either adding or removing (using a PEA antisense cDNA oligomer or anti-enkephalin antibodies) enkephalin peptides from cultured adult thymocytes and examining the effect of this on parameters of activation, such as IL-2 production and proliferation. A role for enkephalin peptides in IL-1 induction of fetal thymocyte maturation will be examined using fetal organ cultures in which enkephalin peptide synthesis or function is blocked. Changes in the constitutive expression of PEA mRNA and in fetal thymocyte subset appearance in response to these modulations will be monitored. IV. Regulation of PEA mRNA expression by B-endorphin (BE), enkephalins, and morphine sulfate (MS) will also be examined. BE, like IL-I, inhibits PEA mRNA expression. Comparison of the effects of IL-1 vs. BE on thymocyte activation and maturation may reveal a role for BE in these processes. Enkephalins will be tested to see if they can regulate the expression of their own mRNA and MS will be studied to compare its effects on PEA mRNA expression to those of the endogenous opioids and IL-1. In summary, these descriptive and mechanistic studies of the expression of PEA mRNA and its peptides will clarify the autocrine/paracrine role of PEA mRNA in thymic maturation and activation.